I live in Ketchikan, Alaska where I garden intensively all over my yard with mostly fruits, and vegetables. This is my second season gardening on my property and it has been a bountiful year so far with garlic, onions, potato’s, lettuce, spinach, raspberries, strawberries, cherries, and gooseberries—to name a few. I love watching the garden evolve and grow over the spring and summer—how bare soil can grow into such lush, delicious greens that fill up your belly. As things grow, so do pests and diseases along with other small problems that always come with gardening and perhaps one of the reasons I love it so! The constant change, day to day and month to month. Everything has been going very well except for one pesky little fly that loves to lay its eggs at the base of the Brassica family i.e. kale, broccoli, kohlrabi, and cabbage.
The root maggot (Delia radicum) is a small, 1/4” fly that deposits her eggs at the base of kale, and other Brassicas. The larvae hatch, then burrow into the soil around the base of the plant and starts chewing away the flesh of the plant to access the sweet flesh located in the cambium layer just under the outer skin. This severally weakens the plant and can even kill a kale if allowed to continue. The tell-tale sign you have root maggots is wilting plants, especially on a sunny day. This is because the plant cannot take up water and nutrients because the root structure has been damaged. If left unchecked root maggots can easily be a perennial problem in the garden, but do not fret as there is always ways to get around those pesky pests with organic measures. I find that with vigilance and with a few mechanical controls, you can produce a bumper crop of cabbages with ease.
How did I control these maggots so they don’t eat my precious plants? I had to get into the flies menacing little brain and find out what makes the root maggot tick (life cycle). Typically root maggots overwinter in the soil (they prefer it to be high in organic matter) and hatch out during spring (in Ketchikan this is usually middle to late May) as the soil warms and kales start really taking off. They find a good host. For me it is always the biggest kale that gets hit first. In about a day or two you can see tiny little white pieces of what seemingly looks like dust at the base of the plants. Almost like a tiny sprinkling of flour, I mean very minuscule amount, and can easily be overlooked if not given a very close inspection (hands and knees with face below the kale leaves). If not scooped up right away they will attack! This happens again around August and is dependent on the weather conditions. The rest of the summer grows along with no problems, as the flies are not flying around at the moment. I have also found that it is extremely localized. One person could have a huge root maggot attack while others have no problems with no protection.
Controlling the pests can be challenging if not prepared for the onslaught. Early prevention is the key. Placing Reemay fabric or plastic over the plants is the best solution and can be taken off by the first week of June. This helps by keeping the flies off the plants and helps the plants by giving them shelter much like a greenhouse or cold frame does. This year I tried making collars out of foil or plastic and wrapping them around the base of each plant. This can be time consuming and found that a couple plants nevertheless got affected and had to be pulled along with a shovel full of precious dirt so the little buggers don’t stay in my garden. The affected plants get tossed in the chicken coup. I have also found that can any kind of man made cover on the soil tends to harbor a lot of slugs as well. I found that a hard clay mud plopped on top of the soil around the base of the plants a good barrier as well, because as the clay dries it becomes an impenetrable layer that the maggots cannot get through. This has become my favorite method as it is easy, and looks better than aluminum foil or Reemay. I want my garden to look good as well as produce food and white Reemay all over my garden did not seem too appealing. To sum it all up, if you want a sure bet, use Reemay or some other type of direct barrier that the flies cannot get through and you are OK with the look. If you are a garden snob who likes to look at your kales growing as you come home from work, then fine clay or a root collar will do the trick but there might be some casualties. If you are attentive you can catch them in the act and squish the little buggers as they surround the collar of your plant. I found this very therapeutic, and satisfying!!
If you find your Brassicas wilting in the sun, know that its might be root maggot season. Having a few backup seedlings in the greenhouse is always a good bet. Happy Gardening!!